diff --git a/classes/ComicPress.inc b/classes/ComicPress.inc
index fa8ff80..4672e65 100644
--- a/classes/ComicPress.inc
+++ b/classes/ComicPress.inc
@@ -142,6 +142,35 @@ class ComicPress {
     }
     return $this->categories_by_id;
   }
+  
+  /**
+   * Turn the tree of comics categories into a string to be fed into wp_query functions.
+   */
+  function get_all_comic_categories_as_cat_string() {
+    if (empty($this->all_comic_categories_as_string)) {
+      $categories = array();
+      foreach ($this->category_tree as $node) {
+        $categories[] = end(explode("/", $node));
+      }
+      $this->all_comic_categories_as_string = implode(",", $categories);
+    }
+    return $this->all_comic_categories_as_string;
+  }
+
+  /**
+   * Return true if the current post is in the comics category or a child category.
+   */
+  function in_comic_category($post_id) {
+    $categories = wp_get_post_categories($post_id);
+    if (is_array($categories)) {
+      foreach ($this->category_tree as $node) {
+        if (in_array(end(explode("/", $node)), $categories)) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
 }
 
 ?>
\ No newline at end of file
diff --git a/functions.php b/functions.php
index 25872d5..c2592a8 100644
--- a/functions.php
+++ b/functions.php
@@ -230,37 +230,8 @@ function get_comic_url($folder = 'comic', $override_post = null, $filter = 'defa
  return false;
 }
 
-/**
- * Turn the tree of comics categories into a string to be fed into wp_query functions.
- */
-function get_all_comic_categories_as_cat_string() {
-  global $all_comic_categories_as_string, $category_tree;
-  if (empty($all_comic_categories_as_string)) {
-    $categories = array();
-    foreach ($category_tree as $node) {
-      $parts = explode("/", $node);
-      $categories[] = end($parts);
-    }
-    $all_comic_categories_as_string = implode(",", $categories);
-  }
-  return $all_comic_categories_as_string;
-}
 
 
-/**
- * Return true if the current post is in the comics category or a child category.
- */
-function in_comic_category() {
-  global $post, $category_tree;
-
-  $comic_categories = array();
-  foreach ($category_tree as $node) {
-    $comic_categories[] = end(explode("/", $node));
-  }
-
-  return (count(array_intersect($comic_categories, wp_get_post_categories($post->ID))) > 0);
-}
-
 // ComicPress Template Functions
 
 function the_comic($filter = 'default') { echo get_comic_url('comic', null, $filter); }
diff --git a/test/ComicPressTest.php b/test/ComicPressTest.php
index ccd4c53..2449123 100644
--- a/test/ComicPressTest.php
+++ b/test/ComicPressTest.php
@@ -93,6 +93,28 @@ class ComicPressTest extends PHPUnit_Framework_TestCase {
     
     $this->assertEquals($expected_tree, $this->cp->sort_comic_categories());
   }
+  
+  function testGetAllComicCategoriesAsCatString() {
+    $this->cp->category_tree = array("0/1", "0/2", "0/3");
+    $this->assertEquals("1,2,3", $this->cp->get_all_comic_categories_as_cat_string());
+  }
+  
+  function providerTestInComicCategory() {
+    return array(
+      array(array(1), false),
+      array(array(2), true)
+    );
+  }
+  
+  /**
+   * @dataProvider providerTestInComicCategory
+   */
+  function testInComicCategory($post_categories, $is_in_category) {
+    $this->cp->category_tree = array('0/2');
+    wp_set_post_categories(1, $post_categories);
+    
+    $this->assertEquals($is_in_category, $this->cp->in_comic_category(1));
+  }
 }
 
 ?>
\ No newline at end of file